U.S. patent number 10,569,948 [Application Number 15/926,674] was granted by the patent office on 2020-02-25 for thermoforming sheets and thermoformed containers prepared therefrom.
This patent grant is currently assigned to Printpack Illinois Inc.. The grantee listed for this patent is Printpack Illinois Inc.. Invention is credited to Harold Stephen Bowen, Rabeh H. Elleithy, Ronald W. Komro, Daniel Clayton Sanders, Amy Whiteman Sherrill.
United States Patent |
10,569,948 |
Sanders , et al. |
February 25, 2020 |
Thermoforming sheets and thermoformed containers prepared
therefrom
Abstract
Forming webs and packages are provided having improved
sealability to peelable lidstocks. The thermoformed containers may
have a mouth having an opening and a flange disposed about the
opening, the flange formed from a forming web and having a
thickness greater than about 12 mils and up to about 80 mils. The
forming web may have a base layer with a skim coating thereon, a
portion of the skim coating being on the flange having a skim
coating thickness from about 2 mils to about 8 mils. A peelable lid
may include a film with an inner lid sealant layer which is sealed
to the portion of the skim coating on the flange, the skim coating
and inner lid sealant layer each having a common polyolefin
majority component, the common polyolefin component being different
than a majority component of the base layer.
Inventors: |
Sanders; Daniel Clayton (West
Point, VA), Sherrill; Amy Whiteman (Mableton, GA),
Elleithy; Rabeh H. (Williamsburg, VA), Bowen; Harold
Stephen (Hayes, VA), Komro; Ronald W. (Smyrna, GA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Printpack Illinois Inc. |
Elgin |
IL |
US |
|
|
Assignee: |
Printpack Illinois Inc. (Elgin,
IL)
|
Family
ID: |
52997561 |
Appl.
No.: |
15/926,674 |
Filed: |
March 20, 2018 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180208382 A1 |
Jul 26, 2018 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15301067 |
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9950849 |
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PCT/US2015/024026 |
Apr 2, 2015 |
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61974995 |
Apr 3, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B
27/08 (20130101); B65D 43/0202 (20130101); B32B
27/32 (20130101); B65D 75/5855 (20130101); B65D
75/26 (20130101); B65D 77/2024 (20130101); B65D
2577/2025 (20130101); B65D 2543/00314 (20130101); B32B
2255/10 (20130101); B32B 2553/00 (20130101); B32B
2255/26 (20130101) |
Current International
Class: |
B65D
75/58 (20060101); B65D 77/20 (20060101); B65D
75/26 (20060101); B32B 27/08 (20060101); B32B
27/32 (20060101); B65D 43/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101209765 |
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Jul 2008 |
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CN |
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101580153 |
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Nov 2009 |
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CN |
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102811924 |
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Dec 2012 |
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CN |
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102985325 |
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Mar 2013 |
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CN |
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203268649 |
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Nov 2013 |
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CN |
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3009007 |
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Feb 1982 |
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DE |
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0305976 |
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Mar 1989 |
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EP |
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1135070 |
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Feb 1999 |
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JP |
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Other References
PCT International Search Report and Written Opinion for
PCT/US2015/024026 dated Oct. 8, 2015 (11 pages). cited by applicant
.
PCT Written Opinion for PCT/US2015/024028 dated Mar. 9, 2016 (8
pages). cited by applicant.
|
Primary Examiner: Thomas; Kareen K
Attorney, Agent or Firm: Eversheds Sutherland (US) LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No.
15/301,067, filed Sep. 30, 2016, which is a U.S. national stage
application of International Application No. PCT/US2015/024026,
filed Apr. 2, 2015, which claims the benefit of U.S. Provisional
Application No. 61/974,995, filed Apr. 3, 2014, the disclosures of
which are incorporated herein by reference.
Claims
We claim:
1. A package comprising: a thermoformed container formed from a
forming web comprising a base layer with a skim coating thereon,
wherein the thermoformed container comprises a mouth having an
opening and including a flange disposed about the opening, the
flange formed from the forming web, wherein a portion of the skim
coating is on the flange; and a peelable lid comprising a film with
an inner lid sealant layer sealed to the portion of the skim
coating on the flange; wherein the skim coating and inner lid
sealant layer have a polyolefin majority component in common, the
polyolefin majority component being different than a majority
component of the base layer, wherein the peelable lid, when peeled,
is separated from the thermoformed container without delamination,
and wherein the skim coating comprises: at least one polyethylene
in an amount from about 35 percent to about 80 percent by weight of
the skim coating; at least one inorganic additive in an amount from
about 1 percent to about 20 percent by weight of the skim coating,
wherein the at least one inorganic additive is selected from the
group consisting of talc, calcium carbonate, fibers, clays, and
combinations thereof; and at least one peelability additive in an
amount from about 5 percent to about 45 percent by weight of the
skim coating, wherein the at least one peelability additive is
selected from the group consisting of polybutylene, polystyrene,
polyesters, and combinations thereof.
2. The package of claim 1, wherein the flange has a thickness
greater than about 12 mils and up to about 80 mils.
3. The package of claim 1, wherein the skim coating has a thickness
of from about 2 mils to about 8 mils.
4. The package of claim 1, wherein the forming web further
comprises an intermediate layer disposed between the base layer and
the skim coating, a portion of the intermediate layer of the flange
having a thickness comprising from about 5 percent to about 50
percent of the thickness of the flange.
5. The package of claim 4, wherein the intermediate layer comprises
a different material than that of the base layer and ties the skim
layer to the base layer.
6. The package of claim 4, wherein the intermediate layer comprises
a polyethylene and the base layer is selected from the group
consisting of a polypropylene, polystyrene, polyvinylidene
chloride, ethyl vinyl acetate (EVA) copolymer, and combinations
thereof.
7. The package of claim 1, wherein the skim coating and inner lid
sealant layer each comprise: at least one polyethylene in an amount
from about 35 percent to about 80 percent by weight; at least one
inorganic additive in an amount from about 1 percent to about 10
percent by weight, wherein the at least one inorganic additive is
selected from the group consisting of talc, calcium carbonate,
fibers, clays, and combinations thereof; and at least one
peelability additive in an amount from about 10 percent to about 20
percent by weight, wherein the at least one peelability additive is
selected from the group consisting of polybutylene, polystyrene,
polyesters, and combinations thereof.
8. The package of claim 1, wherein the inner lid sealant layer is
sealed to the entire portion of the skim coating on the flange.
9. A package comprising: a thermoformed container formed from a
forming web comprising a base layer with a skim coating thereon,
wherein the thermoformed container comprises a mouth having an
opening and including a flange disposed about the opening, the
flange formed from the forming web, wherein a portion of the skim
coating is on the flange; and a peelable lid comprising a film with
an inner lid sealant layer sealed to the portion of the skim
coating on the flange; wherein the skim coating and inner lid
sealant layer have a polyolefin majority component in common, the
polyolefin majority component being different than a majority
component of the base layer, wherein the inner lid sealant layer is
sealed to the entire portion of the skim coating on the flange, and
wherein the skim coating comprises: at least one polyethylene in an
amount from about 35 percent to about 80 percent by weight of the
skim coating; at least one inorganic additive in an amount from
about 1 percent to about 20 percent by weight of the skim coating,
wherein the at least one inorganic additive is selected from the
group consisting of talc, calcium carbonate, fibers, clays, and
combinations thereof; and at least one peelability additive in an
amount from about 5 percent to about 45 percent by weight of the
skim coating, wherein the at least one peelability additive is
selected from the group consisting of polybutylene, polystyrene,
polyesters, and combinations thereof.
10. The package of claim 9, wherein the flange has a thickness
greater than about 12 mils and up to about 80 mils.
11. The package of claim 9, wherein the skim coating has a
thickness from about 2 mils to about 8 mils.
12. The package of claim 9, wherein the forming web further
comprises an intermediate layer disposed between the base layer and
the skim coating, a portion of the intermediate layer of the flange
having a thickness comprising from about 5 percent to about 50
percent of the thickness of the flange.
13. The package of claim 12, wherein the intermediate layer
comprises a different material than that of the base layer and ties
the skim layer to the base layer.
14. The package of claim 13, wherein the intermediate layer
comprises a polyethylene and the base layer is selected from the
group consisting of a polypropylene, polystyrene, polyvinylidene
chloride, ethyl vinyl acetate (EVA) copolymer, and combinations
thereof.
15. The package of claim 9, wherein the skim coating and inner lid
sealant layer each comprise: at least one polyethylene in an amount
from about 35 percent to about 80 percent by weight; at least one
inorganic additive in an amount from about 1 percent to about 10
percent by weight, wherein the at least one inorganic additive is
selected from the group consisting of talc, calcium carbonate,
fibers, clays, and combinations thereof; and at least one
peelability additive in an amount from about 10 percent to about 20
percent by weight, wherein the at least one peelability additive is
selected from the group consisting of polybutylene, polystyrene,
polyesters, and combinations thereof.
16. The package of claim 9, wherein the peelable lid, when peeled,
is separated from the thermoformed container without
delamination.
17. A forming web adapted to form an easy peelable seal with a
lidstock upon heat sealing, wherein the lidstock comprises an inner
lid sealant layer, the forming web comprising: a base layer
comprising a thermoplastic polymer; and a skim coating thereon,
wherein the skim coating and the inner lid sealant layer have a
polyolefin majority component in common, the polyolefin majority
component being different than a majority component of the
thermoplastic polymer of the base layer, wherein the forming web
has a thickness from about 17 mils to about 90 mils and configured
to form a thermoformed container comprising a mouth having an
opening and including a flange disposed about the opening, the
flange formed from the forming web and having a thickness greater
than about 12 mils and up to about 80 mils, a portion of the skim
coating being on the flange and having a skim coating thickness
from about 2 mils to about 8 mils.
18. The forming web of claim 17, wherein the skim coating comprises
at least one polyethylene in an amount from about 35% to about 80%
by weight of the skim coating, at least one inorganic additive in
an amount from about 1% to about 20% by weight of the skim coating,
in which the at least one inorganic additive is selected from the
group consisting of talc, calcium carbonate, fibers, clays, and
combinations thereof, and at least one peelability additive in an
amount from about 5% to about 45% by weight of the skim coating, in
which the at least one peelability additive is selected from the
group consisting of polybutylene, polystyrene, polyesters, and
combinations thereof.
19. A package comprising: a thermoformed container formed from a
forming web comprising a base layer with a skim coating thereon,
wherein the thermoformed container comprises a mouth having an
opening and including a flange disposed about the opening, the
flange formed from the forming web, wherein a portion of the skim
coating is on the flange; and a peelable lid comprising a film with
an inner lid sealant layer sealed to the portion of the skim
coating on the flange; wherein the skim coating and inner lid
sealant layer have a polyolefin majority component in common, the
polyolefin majority component being different than a majority
component of the base layer, wherein the inner lid sealant layer is
sealed to the entire portion of the skim coating on the flange, and
wherein the peelable lid, when peeled, is separated from the
thermoformed container without delamination.
20. The package of claim 19, wherein the skim coating and inner lid
sealant layer each comprise: at least one polyethylene in an amount
from about 35 percent to about 80 percent by weight; at least one
inorganic additive in an amount from about 1 percent to about 10
percent by weight, wherein the at least one inorganic additive is
selected from the group consisting of talc, calcium carbonate,
fibers, clays, and combinations thereof; and at least one
peelability additive in an amount from about 10 percent to about 20
percent by weight, wherein the at least one peelability additive is
selected from the group consisting of polybutylene, polystyrene,
polyesters, and combinations thereof.
Description
BACKGROUND
The present application relates to coextruded sheets adapted for
use in form, fill and seal packaging operations and packages
manufactured from such sheets.
Form, fill and seal (FFS) packaging is widely used to package a
broad variety of products, including disposable medical devices,
food stuffs and similar products. In one type of FFS packaging,
materials corresponding to a lidstock for packages and a bottom or
forming web are supplied in rolls. The forming web material is
indexed from the roll into a heating zone where it is heated to
forming temperatures. The heated forming web material is then
either immediately formed or indexed into a forming station area
where multiple box or cup shaped compartments are formed from the
forming web using any one of a number of thermoforming techniques
(i.e., drape forming, matched mold forming, vacuum forming or
pressure bubble-plug assist vacuum forming). Other thermoforming
methods are also known.
After forming, the bottom web is typically chilled or cooled and
the product to be packaged is inserted into the individual formed
compartments. The lidstock material is then applied to the forming
web, sealing the compartments. The lidstock material may be sealed
to the upper perimeter of the individual compartments using an
adhesive and/or by heat sealing. These formed serially connected
packages can then be cut from the web and trimmed to the desired
final shape. Secondary functions that are selectively integrated
into the process (i.e., printing or decorating) either before or
after forming, may include embossing, notching, slotting, punching,
labeling, counting and stacking.
Although these packages provide numerous advantages, the material
incompatibility of the formed bottom web and lidstock can result in
delamination, stringing, and/or peeling of the lidstock from the
formed bottom web. In addition, many materials used in these
packages are only suitable for use in limited applications and
cannot withstand the wide range of temperatures, times, and
pressures used during many sealing and sterilization processes.
Thus, there exists a need for improved sheets useable as lidstock
and forming webs in form, fill and seal applications.
SUMMARY
In one aspect, thermoformed containers are provided having a mouth
with an opening and a flange disposed about the opening, the flange
formed from a forming web and having a thickness greater than about
12 mils and up to about 80 mils. The forming web may have a base
layer with a skim coating thereon, a portion of the skim coating
being on the flange having a skim coating thickness from about 2
mils to about 8 mils. A peelable lid may include a film with an
inner lid sealant layer which is sealed to the portion of the skim
coating on the flange, the skim coating and inner lid sealant layer
each having a common polyolefin majority component, the common
polyolefin component being different than a majority component of
the base layer.
In another aspect, a forming web is provided that is adapted to
form an easy peelable seal with a lidstock upon heat sealing. The
forming web may include a base layer with a thermoplastic polymer
and a skim coating thereon, the forming web being configured to
form a thermoformed container with a mouth having an opening and
including a flange disposed about the opening, the flange formed
from the forming web and having a thickness greater than about 12
mils and up to about 80 mils. A portion of the skim coating may be
disposed on the flange and have a skim coating thickness from about
2 mils to about 8 mils, the skim coating including a common
polyolefin majority component as that of an inner lid sealant layer
of the lidstock, the common majority polyolefin component being
different than a majority component of the thermoplastic polymer of
the base layer.
Additional aspects will be set forth in part in the description
which follows, and in part will be obvious from the description, or
may be learned by practice of the aspects described below. The
advantages described below will be realized and attained by means
of the elements and combinations particularly pointed out in the
appended claims. It is to be understood that both the foregoing
general description and the following detailed description are
exemplary and explanatory only and are not restrictive.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a cross-sectional illustration of a thermoformed
container and lid according to an embodiment.
FIG. 2 is an enlarged cross-section of a portion of the
thermoformed container and lid illustrated in FIG. 1.
FIG. 3 is a graph comparing the burst pressure of thermoformed
containers prepared in the Examples.
DETAILED DESCRIPTION
Embodiments of the present description address the above-described
needs by providing thermoformed containers having improved
compatibility with peelable lidstocks. The improved compatibility
results from the sealing of a skim coating of the thermoformed
container and an inner sealant layer of the peelable lidstock
(i.e., the bottom layer of the peelable lidstock that is contacted
with the skim coating of the thermoformed container). The skim
coating and inner lid sealant layer each comprise a common
polyolefin majority component, thereby eliminating or, at the very
least, significantly reducing incompatibility between the base
layer of the thermoformed web and the peelable lidstock,
particularly when the inner sealant layer of the peelable lidstock
has a different majority polymer component than the thermoformed
container.
As used herein, "skim coating" and "skim layer" are used
interchangeably to refer to a very thin layer disposed on the
forming web having a different majority polymer component than the
forming web. The skim coating may have a skim coating thickness
from about 0.25 to about 25% of the thickness of the forming web.
For example, in certain embodiments the skim coating thickness is
from about 2 mils to about 8 mils, from about 2 mils to about 6
mils, from about 2 mils to about 4 mils, or from about 2 mils to
about 3.5 mils.
The thermoformed containers are formed from a forming web
comprising the skim coating disposed on a base layer. The
thermoformed container may be a tray or cup in any desired shape
formed by thermoforming the forming web. The thermoformed
containers generally include a mouth with an opening and flange
disposed about the opening to which the peelable lidstock is
sealed. The flange generally has a thickness greater than about 12
mils, greater than about 17 mils, or greater than about 20 mils.
For example, the flange may have a thickness greater than about 20
mils and up to about 80 mils, from about 25 mils to about 75 mils,
from about 30 mils to about 70 mils, from about 30 mils to about 60
mils, from about 30 mils to about 50 mils, or any amount
therebetween. A portion of the skim coating on the flange has a
skim coating thickness from about 2 mils to about 8 mils, from
about 2 mils to about 6 mils, from about 2 mils to about 4 mils,
from about 2 mils to about 3.5 mils, from about 2 mils to about 3
mils, or any amount therebetween. Those skilled in the art will
appreciate that the forming web prior to thermoforming generally
has a thickness greater than that of the thermoformed container
(e.g., the forming web will have a thickness from about 5 mils to
about 10 mils greater than the flange, from about 7 mils to about
10 mils greater than the flange, and the like). Thus, in certain
embodiments the forming web with a thickness greater than about 25
mils is configured to form a thermoformed container with a flange
having a thickness greater than about 20 mils. Similarly, a forming
web with a thickness from about 30 mils to about 90 mils may be
configured to form a thermoformed container with a flange having a
thickness from about 20 mils to about 80 mils.
The base layer of the forming web often comprises a material that
is different than that of the peelable lidstock and may be a
monolayer or multilayer material. For example, in certain
embodiments the base layer may comprise polystyrene, polypropylene,
polyvinylidene chloride, ethyl vinyl acetate (EVA) copolymer, or
combinations thereof. The forming web of the thermoformed container
may further comprise one or more intermediate layers disposed
between the base layer and the skim coating. A portion of the one
or more intermediate layers of the flange may have a thickness from
about 2% to about 95% of the thickness of the flange, from about 5%
to about 50% of the thickness of the flange, from about 10% to
about 40% of the thickness of the flange, from about 10% to about
30% of the thickness of the flange, or from about 10% to about 20%
of the thickness of the flange. For example, in embodiments the
portion of the one or more intermediate layers of the flange may
have a thickness from about 0.5 mils to about 76 mils, from about 5
mils to about 20 mils, from about 5 mils to about 10 mils, or
amounts therebetween. In certain embodiments, the intermediate
layer comprises a different material than that of the base layer
and ties the skim coating to the base layer (i.e., a "tie layer").
In certain embodiments, the tie layer has an affinity to both the
base layer and the skim coating so as to tie the base layer to the
skim coating and reduce likelihood that the skim coating
delaminates from the base layer. Thus, the overall composition of
the tie layer may be different from both the composition of the
base layer and the composition of the skim coating. For example,
the intermediate layer may comprise a polyethylene (LDPE, LLDPE,
and the like). In addition or in the alternative, the intermediate
layer may function to reduce the seal initiation temperature and/or
provide an improved moisture barrier.
In instances where a high barrier thermoformed container is
desired, the base layer and/or one or more intermediate layers of
the forming web may include a barrier layer to extend the shelf
life of the products to be packaged in the thermoformed container.
For example, barrier layers may be used where products to be
packaged are sensitive to certain gases, or loss of volatiles,
flavors, or aromas. Materials suitable for use as barrier materials
are known in the art, including ethylene vinyl alcohol, nylon,
polyvinylidene chloride, liquid crystalline polymer, or any
combination thereof. The barrier layers also may include barrier
enhancing additives, such as nano-additives or oxygen
scavengers.
The skim coating of the forming web generally comprises a material
that is easy to melt, has good flow properties, and is readily
compatible with the inner lid sealant layer of the peelable
lidstock. In certain embodiments, the skim coating and the inner
lid sealant layer each comprise sealant compositions having a
common polyolefin majority component, the common polyolefin
majority component being different than a majority component of the
base layer. As used herein, a "majority component" is the component
that is present in the greatest quantity. In exemplary embodiments,
the common polyolefin majority component of the sealant
compositions of the skim coating and inner lid sealant layer
comprises from about 40% to about 100% by weight. For example, the
common polyolefin majority component may comprise a polyethylene or
blend of two or more polyethylenes (i.e., a high density
polyethylene (HDPE) and low density polyethylene (LDPE)), the total
amount of the common polyolefin majority component comprising the
blend of two or more polyethylenes may be up to about 80% to about
100% by weight of the sealant compositions. In an embodiment, the
HDPE and LDPE are present in a ratio from 80:20 to 20:80, 60:40 to
about 40:60, or ratios therebetween. For example, the HDPE may be
present in an amount from about 40% to about 60% weight of the
sealant compositions and the LDPE may be present in an amount from
about 20% to about 40% by weight of the sealant compositions.
The composition of the sealant compositions may further comprise
one or more additives, such as a peelability additive capable of
improving peelability of the lid, and may be either immiscible or
partially miscible in the main resin matrix. Non-limiting examples
of additives that may be used in the sealant compositions of the
skim coating and inner lid sealant layer include inorganic
additives such as talc, calcium carbonate, fibers, clay or
nano-alternatives thereof, and organic additives such as
polybutadiene, polystyrene, and polyesters. The one or more
additives may be present in the compositions of the sealant
compositions in amounts from about 0.01% to about 50% by weight,
with the total amount of the one or more additives comprising up to
about 50% by weight of the compositions. In certain embodiments,
the sealant compositions of the skim coating and inner lid sealant
layer may further comprise at least one peelability additive in an
amount from about 0.1% to about 45% by weight of the sealant
compositions. For example, the sealant compositions may comprise at
least one inorganic additive in an amount from about 1% to about
20% by weight of the sealant compositions and at least one organic
peelability additive in an amount from about 5% to about 45% by
weight of the sealant compositions. In another embodiment, the
sealant compositions may comprise at least one inorganic additive
in an amount from about 1% to about 10% by weight of the sealant
compositions and at least one organic peelability additive in an
amount from about 10% to about 20% by weight of the sealant
compositions.
The forming web may be prepared using appropriate methods known to
those skilled in the art. For example, the forming web may be
extruded or laminated using methods such as multimanifold die
coextrusion, feedblock technology, extrusion coating, and thermal
lamination. Methods for making thermoformed containers also are
known in the art, and may include (i) providing the forming web;
(ii) heating the forming web; (iii) drawing the heated forming web
into a mold to shape the material. The processes of making the
forming web and thermoformed containers may be performed in series
(i.e., in-line thermoforming) or independently (i.e., off-line
thermoforming). For example, in certain embodiments in which the
base layer comprises polystyrene, the forming web may be rolled and
stored for later processing of the forming web into the
thermoformed container. In other embodiments in which the base
layer comprises a polypropylene, the thermoforming of the forming
web may be performed in-line to produce the desired thermoformed
container shape.
Advantageously, embodiments of the present application permit
sealing of the lids to the thermoformed container at lower
temperatures and pressures and shorter dwell times; however, those
of ordinary skill in the art will appreciate that the particular
properties used for sealing the lids to the thermoformed containers
will vary depending on the products being packaged and equipment
being used. For example, the lids may be sealed to the thermoformed
containers at temperatures from about 175.degree. C. to about
235.degree. C., pressures from about 20 psi to about 110 psi, and
over a dwell time from about 0.3 seconds to about 4 seconds.
An exemplary embodiment of a package 10 is illustrated in FIG. 1.
The package 10 includes a cup-shaped thermoformed container 12 with
a mouth 14 having an opening and a flange 16 disposed about the
opening. A peelable lidstock 18 is sealed to the flange 16 of the
thermoformed container. The thermoformed container 12 is formed
from a forming web including a base layer 20, an intermediate "tie"
layer 22, and a skim coating 24. The peelable lidstock includes one
or more layers of flexible film 28 (i.e., polyolefins, metallized
polyolefins, papers, foils, and the like) with an inner lid sealant
layer 26 sealed to the skim coating 24 of the flange.
The packages of the present application advantageously provide an
easy peel lid/thermoformed container system that is optimized to
seal at low temperature over a wide range of temperatures and
pressures. Such systems provide numerous advantages for food or
medical packaging applications, including a wide range of sealing
temperature; short sealing time; an easy-to-peel lid; a
thermoformed container/lid system with high burst strength;
suitable for high-temperature and moisture processes, such as steam
sterilization; and/or presents a clean appearance when peeled, with
minimal or no obvious stringing, fuzziness, tearing, or
delamination. Such systems also may provide further advantages for
medical applications, including being suitable for use in multiple
sterilization methods (e.g., ETO, vapor hydrogen peroxide
sterilization, and radiation sterilization). Additionally, when
breathable material, such as a spunbonded nonwoven polyolefin web
is used for the peelable lid (e.g., Tyvek.RTM.), there may be a
reduced potential for a breach of the microbial barrier, and
increased breathability of the uncoated lid than the conventional
coated lids that have been used.
Embodiments of the present description are further illustrated by
the following examples, which are not to be construed in any way as
imparting limitations upon the scope thereof. On the contrary, it
is to be clearly understood that resort may be had to various other
embodiments, modifications, and equivalents thereof which, after
reading the description herein, may suggest themselves to those
skilled in the art without departing from the spirit of the present
invention and/or the scope of the appended claims. Unless otherwise
specified, quantities referred to by percentages (%) are by weight
(wt %).
EXAMPLES
Easy peel lidding/cup systems were produced for testing using
various formulations of lidstock and sheets for thermoforming the
cups. Three lidstock films were produced from multilayer films,
each having the structure:
TABLE-US-00001 oriented polyethyelene terephthalate (OPET) white
polyethylene (PE) white acrylic acid copolymer (EAA) Foil
Sealant
Three different sealants were prepared from blends of ethylene
acrylic acid copolymers (EAA), high density polyethylene (HDPE),
low density polyethylene (LDPE), polybutylene (PB), and talc, as
follows:
TABLE-US-00002 Sealant 96 Sealant 97 Sealant 98 8# EAA-8# #5 EAA-5#
8# EAA-8# HDPE 49 49 51 LDPE 29 29 29 PB 16 16 10 Talc 6 6 10
Four different polystyrene cups were prepared from a polystyrene
film coextruded with LDPE and either no skim layer (control) or a 2
mil skim layer using the sealant compositions summarized in the
table below.
TABLE-US-00003 Cup 01 Cup 42 Cup 43 Cup 50 PS PS PS PS 7 mil LDPE 9
mil LDPE 7 mil LDPE 7 mil LDPE 2 mil Skim Layer -- 2 mil Skim Layer
2 mil Skim Layer (Sealant (LLDPE) (ULDPE) 96/97/98)
The lids were sealed to the cup at temperatures of 350, 375, or
400.degree. F.; pressures of 20 or 30 psi; and a dwell time of 0.5
or 1.0 seconds. The burst pressures were measured for each
container, and exemplary data of the thermoformed containers sealed
at 400.degree. F., 30 psi, and 1.0 second are illustrated in FIG.
3.
The cups produced using the skim layers had a high burst pressure
and sealed at a lower temperature than cups without the skim layer.
In addition, the cups with the skim layers had a very low stringing
tendency and were not prone to delamination, properties consistent
with the desired easy peel functionality.
While the invention has been described in detail with respect to
specific embodiments thereof, it will be appreciated that those
skilled in the art, upon attaining an understanding of the
foregoing, may readily conceive of alterations to, variations of,
and equivalents to these embodiments. Accordingly, the scope of the
present invention should be assessed as that of the appended claims
and any equivalents thereof.
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